Field of the Invention
Embodiments relate to methods and systems for establishing a telecommunication connection between a calling subscriber and a target subscriber.
Background of the Related Art
By means of the callback function CCBS (Completion of Call to a Busy Subscriber), a caller, also called a calling subscriber, can have a switching unit establish a telecommunication connection to a temporarily busy terminal of a call recipient, also called a target subscriber. A calling subscriber who receives a busy signal from his target subscriber's terminal the first time he calls can leave a CCBS-REQ callback request in the switching unit before ending his call, e.g., by hanging up the receiver, using the keyboard of his terminal or by means of a message. If the target subscriber's temporarily busy terminal becomes free, e.g., by means of the completion of an ongoing conversation on the terminal, the calling subscriber's terminal receives a notification through the switching unit about the end of the ongoing conversation on the target subscriber's terminal. The calling subscriber's terminal then informs the calling subscriber, by means of a signal such as a special ring tone, that the target subscriber's terminal is no longer busy. The switching unit's call to the calling subscriber's terminal to inform the calling subscriber that the target subscriber's terminal is no longer busy is considered a callback. If the calling subscriber accepts this callback, which can be done by lifting a phone receiver, for example, then the switching unit calls the target subscriber again. The call made to the target subscriber by the switching unit to establish a connection between the calling subscriber and the target subscriber is considered a second call. CCBS cannot be used if the target subscriber refuses the call placed by the switching unit or if the target subscriber's switching center does not support callback functions.
Using the CCNR (Completion of Call on No Reply) callback function, a calling subscriber can have a switching unit establish a telecommunication connection with a target subscriber who does not accept a first call from the calling subscriber. A calling subscriber whose target subscriber is using a terminal that gives a ringback tone to the calling subscriber, when the calling subscriber's call is not accepted, can activate the CCNR callback function by leaving a CCNR-REQ callback request in the switching unit before the end of the first call, e.g., by hanging up the receiver, using the keyboard of his terminal or by means of a message. If the target subscriber ends a conversation after activation of CCNR, e.g., by hanging up the telephone receiver on his terminal, the calling subscriber's terminal receives a notification of the end of the target subscriber's conversation through the switching unit. The terminal then informs the calling subscriber, by means of a signal such as a special ring tone, that the target subscriber's terminal can be reached. The switching unit's call to the calling subscriber's terminal to inform the calling subscriber that the target subscriber's terminal can be reached is also considered a callback with CCNR, comparable to the definition of a callback for CCBS. If the calling subscriber accepts this callback, e.g., by lifting the receiver of his terminal, then the calling subscriber will be connected with the desired target subscriber's terminal by the switching unit in a second call. CCNR cannot be used if the target subscriber refuses the call placed by the switching unit or if the target subscriber's switching center does not support callback functions.
CCBS-REQ, CCNR-REQ callback requests that are left in the switching unit using the CCBS and/or CCNR callback functions are deleted from the switching unit with no notification to the calling subscriber if the callback fails or after a preset length of time stored in the switching unit, e.g., one hour. A standard switching unit can process multiple CCBS-REQs and/or CCNR-REQs in the order in which they were placed in the switching unit.
EP 1 156 648 A2 describes a method for establishing a telecommunication connection in which, if a second call is placed as an answer to the requested callback from a calling terminal to a target terminal and the target terminal becomes busy again in the meantime, the call is placed in a waiting area assigned to a switching unit for at least a preset length of time, in order to wait for the target terminal to become free again, without the calling terminal receiving a busy signal. During the time that the second call directed from the calling terminal to the target terminal is held in the switching unit's waiting area, a ringing tone, hold music, recorded voice message, or other suitable indicator is played to the calling terminal. As soon as the target terminal becomes free, within the preset length of time, the connection to the target terminal is displayed on the calling terminal. A disadvantage is that, during the time that the second call is being held in the switching unit's waiting area, the calling terminal is busy for other calling subscribers, although no communication occurs via the connection established with the second call. If the hold time for the target terminal to become free again, i.e., the preset length of time in which the second call is held in the switching unit's waiting area, expires without success, a connection between the calling terminal and the target terminal through the requested callback is not established.
Proceeding from the foregoing, the problem addressed by the invention is that of creating a method for establishing a telecommunication connection that avoids the disadvantages of the prior art. In particular, it should be a method for establishing a telecommunication connection in which a connection is established between the calling subscriber and the target subscriber by means of the callback requested by the calling subscriber, wherein the calling subscriber remains reachable by other calling subscribers until the connection to the target subscriber is established.